JP2020059874A - Method for producing ferrous member - Google Patents

Abstract

To provide a method that makes it possible to produce conveniently a ferrous member that has a passive film excellently formed on its surface, and shows an excellent rust-prevention performance, and also provide a natural potential measuring method for evaluating the formation state of a passive film on a ferrous material surface.SOLUTION: A method for producing a ferrous member includes the step of making the ferrous member and a nitrite vaporable rust inhibitor coexist in a closed space controlled to low humidity. A method of measuring a self potential of a ferrous material includes the step of, while degassing an electrolyte solution, immersing an electrode composed of the ferrous material and a reference electrode in an electrolyte solution, and measuring a potential difference between the electrodes.SELECTED DRAWING: None

Description

  TECHNICAL FIELD The present invention relates to a method for easily producing an iron-based member having a good passivation film on the surface and excellent in rust prevention performance.

  In order to enhance the anticorrosion performance of iron-based members, a method of immersing the iron-based members in an aqueous solution of a rust preventive agent containing nitrite ion was the mainstream. However, this method requires special surface treatment equipment such as a tank for the rust preventive solution and a tank for washing with water after that, waste liquid needs to be treated, and iron-based members with complicated shapes are required. Then, there is a problem that it may be difficult to remove the aqueous solution of the rust preventive agent in the gap. When the aqueous solution of the rust preventive remains in the gap, the corrosion is rather accelerated. Further, when the iron-based member is a huge iron plate or iron column, the surface treatment facility becomes large in scale and a large amount of waste liquid is generated. Further, there are cases in which an iron-based member having a complicated shape cannot be effectively treated for rust prevention.

  Therefore, a nitrite-based vaporizable rust preventive agent capable of releasing nitrite ions exhibiting a rust preventive action has been developed. If it is a nitrous acid-based rust preventive agent, the vaporized rust preventive component acts on the iron-based member, so large-scale surface treatment equipment is not required, no waste liquid is generated, and the rust preventive agent aqueous solution remains. There is no room.

  Among the nitrite-based volatile rust preventives, the metathesis type volatile rust preventives are those which undergo metathesis by water in the environment to generate strongly volatile ammonium nitrite, diffuse nitrite ions, and have a metal surface. It is considered that the rust prevention effect is exerted by absorbing the generated ammonia into the dew condensation water and alkalizing it, and it shows that a large amount of vaporized nitrite gas is released under high humidity such as 90% and 100% relative humidity. (Non-Patent Document 1).

  Therefore, as a nitrous acid-based vaporizing rust preventive agent, while the metal releases nitrite gas under high humidity where it is easy to rust, the release of nitrite gas is suppressed under low humidity where rust hardly occurs. It was said to be efficient and excellent (Patent Documents 1 to 4).

JP2012-207360A JP, 2011-47028, A JP, 2010-285661, A JP, 2006-45643, A

Arimatsu Ippiko et al., Rust prevention management, 2007, p. 15-19

As described above, a vaporizable rust inhibitor that develops a rust preventive effect by diffusing nitrite ions by utilizing moisture in the environment has been developed. Since more nitrite ions are released in a high humidity environment where rust is likely to occur, it was considered that the one that does not release nitrite ions in a low humidity environment where rust is hard to occur is efficient. Therefore, the conventional nitrite-based vaporizable rust preventive agent is generally used in a closed environment including both metal members to be rust-prevented in order to effectively utilize nitrite ions.
However, a more efficient anticorrosion treatment method is always desired in the field.
Therefore, an object of the present invention is to provide a method capable of easily producing an iron-based member having a good passivation film formed on the surface and excellent in rust prevention performance. Another object of the present invention is to provide a method for measuring the spontaneous potential for evaluating the formation state of the passive film on the surface of the iron-based material.

The present inventors have conducted extensive studies to solve the above problems. As a result, conventionally, the performance of nitrite-based vaporizing rust preventive agent has been confirmed by the amount of nitrite ion and ammonia gas released under high humidity. While it was thought that it was not necessary to exert the effect, the passivation film on the surface of the iron-based member was better formed in a low humidity environment, and it was found that the rust preventive action continues even in an open environment, The present invention has been completed.
The present invention will be described below.

[1] A method for manufacturing an iron-based member, comprising:
A method comprising the step of allowing the iron-based member and a nitrite-based vaporizable rust preventive agent to coexist in a closed space controlled to have low humidity.
[2] The method according to [1] above, wherein the relative humidity in the closed space is 45% or less.
[3] The nitrite-based vaporizable rust inhibitor is one or more nitrites selected from the group consisting essentially of dicyclohexylamine nitrite, diisopropylamine nitrite, sodium nitrite, and potassium nitrite. The method according to [1] or [2] above, which comprises:
[4] The method according to any one of [1] to [3] above, wherein the nitrous acid-based vaporizable rust preventive agent contains an ammonium salt.
[5] The method according to any one of [1] to [4] above, wherein the iron-based member and the nitrite-based vaporizable rust inhibitor are allowed to coexist for 1 day or more.
[6] The method according to any one of [1] to [5] above, wherein the temperature at which the iron-based member and the nitrite-based vaporizable rust inhibitor coexist is 5 ° C or higher and 50 ° C or lower.
[7] The method according to any one of [1] to [6] above, wherein the difference between the surface potential of the iron-based member before the above step and the surface potential of the iron-based member after the above step is +90 mV or more.
[8] A method for measuring the spontaneous potential of an iron-based material, comprising:
A method comprising immersing an electrode made of the iron-based material and a reference electrode in an electrolyte solution while degassing the electrolyte solution, and measuring a potential difference between the electrodes.

  Conventionally, the anticorrosive action of a nitrite-based vaporizable anticorrosive agent has been evaluated by the amount of nitrite ion or ammonia gas released. The reason for this is that the vaporizable rust preventive agent was considered to exhibit a rust preventive effect only in a closed space. Regarding the anticorrosive action of the nitrous acid-based vaporizable anticorrosive agent, it is considered that the thickness of the passivation film of the iron-based material treated thereby is measured by X-ray photoelectron spectroscopy (XPS). It is impossible to clearly define the boundary between the dynamic film and the layer containing only iron-based material, and accurate evaluation cannot be performed. Furthermore, when a passive film is formed on the surface of the iron-based material, the anodic reaction is suppressed. Therefore, it is possible to measure the spontaneous potential as an evaluation criterion for the passive film. However, since the iron-based material gradually corrodes in the electrolyte solution for measuring the natural potential, the potential difference from the reference electrode cannot be measured stably and accurate evaluation cannot be performed.

  On the other hand, the present inventors have completed an accurate method of measuring the self-potential, and thereby made it possible to accurately evaluate the stability of the iron-based material due to the passive film.

  INDUSTRIAL APPLICABILITY The method for manufacturing an iron-based member according to the present invention forms a passivation film on the surface of the iron-based member in a favorable manner, and significantly improves its rust prevention performance. As a result, the conventional iron-based member product was distributed while being hermetically packaged together with the vaporizable rust preventive agent, because an excellent passivation film is formed on the iron-based member manufactured by the method of the present invention. Excellent rust prevention performance even in open environment. Therefore, the present invention is industrially extremely excellent as a technique capable of producing an iron-based member having excellent rust prevention performance.

FIG. 1 is an appearance photograph of an iron-based member test piece showing the results of the corrosion resistance performance test. FIG. 1 (1) is an appearance photograph of a test piece that has been subjected to the vapor phase rust prevention treatment according to the present invention, and FIG. 1 (2) is an appearance photograph of a control test piece.

  The method for producing an iron-based member according to the present invention includes the step of allowing the iron-based member and the nitrite-based vaporizable rust preventive agent to coexist in a closed space adjusted to have low humidity.

  The material forming the iron-based member is not particularly limited as long as Fe is the main component. “Mainly containing Fe” means that the proportion of Fe in the material is 50 mass% or more. The proportion is preferably 60% by mass or more, and more preferably 70% by mass or more. Examples of iron-based member materials containing components other than Fe include, for example, chrome steel steel (SCr material), manganese steel steel material (SMn material), manganese chrome steel steel material (SMnC material), chrome molybdenum steel steel material (SCM material), nickel. Chrome steel steel (SNC material), nickel chromium molybdenum steel material (SNCM material), aluminum chromium molybdenum steel material (SACM material), carbon steel material (SC material), stainless steel material (SUS material), high carbon chromium bearing steel material (SUJ material) and the like. It should be noted that, on a surface of a general iron-based material, a passivation film is naturally formed to some extent unless under a special environment, but according to the method of the present invention, a more excellent passivation film is formed. Can be effectively formed.

  The iron-based member is a component that is made of the above-mentioned material and is used to assemble a structure. However, as long as it constitutes some kind of structure, iron plates and iron columns are also included.

  In the method of the present invention, the inside of the closed space in which the iron-based member and the nitrite-based vaporizable rust preventive coexist is adjusted to low humidity. The degree of "low humidity" may be appropriately adjusted within a range in which a sufficient passivation film is formed on the surface of the iron-based member, but can be set to, for example, 45% or less in relative humidity. The relative humidity is preferably 40% or less, more preferably 35% or less, still more preferably 30% or less, 25% or less or 20% or less. The relative humidity may be measured by a hygrometer based on a conventional method.

  The method for adjusting the humidity in the closed space is not particularly limited, but it is conceivable to use a desiccant such as silica gel, calcium chloride, quick lime, diphosphorus pentoxide, concentrated sulfuric acid, glycerin, or an aqueous glycerin solution. Further, a part or the whole of the closed space may be replaced with an inert gas such as nitrogen gas that does not contain water or has a reduced water content.

  In order to form the closed space, for example, at least the iron-based member and the nitrite-based vaporizable rust preventive may be hermetically packaged with a film or sealed in a case. Examples of the material forming the packaging or case include polyolefins such as polyethylene and polypropylene; metals such as aluminum; glass and the like. In addition, for the purpose of suppressing the permeation of water molecules and oxygen molecules, polyolefin films and sheets are used in polyesters such as polyethylene terephthalate, polyamides such as nylon, chlorine-containing resins such as polyvinylidene chloride and polyvinyl chloride, and metals such as aluminum. Alternatively, a layer formed of a metal oxide such as aluminum oxide may be stacked.

  The thickness of the film or sheet for forming the closed space can be, for example, 20 μm or more. In order to more reliably suppress the permeation of water molecules and oxygen molecules and the disappearance of the vaporized rust preventive component, the thickness is preferably 100 μm or more.

  The nitrite-based vaporizable rust inhibitor is not particularly specified as long as it is a compound or composition containing nitrite ion and ammonium ion or amino cation, but a compound containing nitrite ion and ammonium ion is preferable from the viewpoint of high vapor pressure. . Further, the nitrous acid-based vaporizable rust preventive agent may contain, for example, a nitrite salt and an ammonium salt, and exhibit a rust preventive effect by a hydrolysis reaction utilizing water vapor in the air. The nitrite-based vaporizable rust inhibitor used in the present invention contains at least nitrite and ammonium salt because of its high vapor pressure and good operability, and can release nitrite ions in a closed space. It is preferable to select from

Examples of the nitrite, that is, a salt having a nitrite ion (NO ₂ ⁻ ) include organic amine nitrite and metal nitrite. With these organic amine nitrites and metal nitrites, the hydrometathesis reaction with ammonium salts proceeds efficiently, and excellent rust prevention performance can be obtained. The nitrite may be used alone or in combination of two or more kinds.

  As the organic amine constituting the nitrite of the organic amine, primary to tertiary aromatic amines and primary to tertiary aliphatic amines are preferable. As nitrites of organic amines, nitrites of primary aromatic amines such as aniline; nitrites of secondary cycloaliphatic amines such as dicycloalkylamines; secondary branched chain fatty acids such as diisopropylamine. Group amine nitrites; tertiary amine nitrites, and the like, secondary organic amine nitrites are preferable, and dicycloalkylamine nitrites are more preferable.

  Examples of the metal nitrite include nitrites of alkali metal ions such as lithium ion, sodium ion and potassium ion; nitrite salts of alkaline earth metal ions such as calcium ion; nitrite salts of magnesium ion. Is preferable, and a nitrite of sodium ion is more preferable.

  The content of the nitrite is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more in 100% by mass of the volatile anticorrosive agent. When the content of the nitrite is in this range, it is likely to undergo hydrometathesis together with the ammonium salt, which contributes to the improvement of rust prevention performance. The content of nitrite is preferably 60% by mass or less, more preferably 50% by mass or less.

  When an ammonium salt is used in combination with a nitrite salt as the nitrite-based vaporizable rust preventive agent, a rust preventive substance (ammonium nitrite) is generated by the hydrometathesis of these compounds, so that an excellent rust preventive effect is obtained. The ammonium salt may be used alone or in combination of two or more kinds.

  Examples of the inorganic acid forming the ammonium salt include boric acid, phosphoric acid, carbonic acid, sulfuric acid, hydrochloric acid and the like. Examples of ammonium salts of these inorganic acids include ammonium borate such as ammonium metaborate, ammonium orthoborate, and ammonium tetraborate; monoammonium phosphate, diammonium phosphate, triammonium phosphate, diammonium hydrogenphosphate, etc. Ammonium phosphate; ammonium carbonate such as diammonium carbonate, monoammonium carbonate, ammonium hydrogencarbonate; ammonium sulfate; ammonium chloride and the like. Of these, ammonium borate such as ammonium tetraborate; ammonium phosphate such as diammonium phosphate, triammonium phosphate, diammonium hydrogen phosphate; ammonium carbonate and the like are preferable.

  As the organic acid that constitutes the ammonium salt, a monovalent or divalent or higher carboxylic acid is preferable, and a monovalent or trivalent or lower carboxylic acid is preferable. Specific examples of the organic acid ammonium salt include monovalent aromatic carboxylic acid ammonium salts such as ammonium benzoate, ammonium salicylate, and ammonium p-nitrobenzoate; monovalent aliphatic salts such as ammonium formate and ammonium acetate. Ammonium carboxylic acid salt; Ammonium oxalate salt, diammonium sebacate salt, etc., divalent aliphatic dicarboxylic acid ammonium salt; Divalent ammonium hydroxy acid salt, such as malic acid; Trivalent ammonium hydroxy acid salt, such as ammonium citrate Examples include salt. Of these, ammonium salts of monovalent organic acids and ammonium salts of divalent organic acids are preferable, monovalent aromatic carboxylic acid ammonium salts and divalent aliphatic dicarboxylic acid ammonium salts are more preferable, and ammonium benzoate and sebacine are preferable. More preferred is diammonium acid.

  As the ammonium salt, ammonium salts of inorganic acids such as ammonium carbonate and diammonium hydrogen phosphate; ammonium salts of organic acids such as ammonium benzoate, ammonium salicylate, ammonium p-nitrobenzoate and ammonium sebacate are preferable, and benzoic acid is preferable. Particularly preferred are ammonium and diammonium hydrogen phosphate.

  The content of the ammonium salt is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more in 100% by mass of the volatile rust preventive agent. When the content of the ammonium salt is within this range, it is likely to undergo hydrometathesis together with the nitrite, which contributes to the improvement of rust prevention performance. The amount is preferably 40% by mass or less, more preferably 30% by mass or less.

  Further, in the volatile anticorrosive agent, the content of ammonium salt is preferably 1 mol or more, more preferably 50 mol or more, still more preferably 60 mol or more and 200 mol or less with respect to 100 mol of nitrite. Is preferable, more preferably 150 mol or less, further preferably 100 mol or less. When the contents of ammonium salt and nitrite are in this range, excellent rust preventive action can be exhibited for a long period of time.

  The nitrite-based vaporizable rust preventive agent may contain a hydrogen carbonate metal salt. The inclusion of the hydrogencarbonate metal salt can stabilize the ammonium ion generated by the decomposition of the ammonium salt as the ammonium carbonate metal salt, so that it controls the hydrometathesis reaction of the nitrite and the ammonium salt to prevent the long-term rust prevention ability. Can be demonstrated. When the nitrous acid-based volatile rust preventive agent contains a water retention aid, the use of a hydrogen carbonate metal salt suppresses the hydrometalysis reaction due to the water content of the water retention aid and stabilizes the volatile rust inhibitor. It can also improve the sex. Further, even when the nitrous acid-based vaporizable rust preventive agent is formed into a tablet shape or a granular shape, it is possible to improve the shape retention and prevent disintegration by including the metal hydrogen carbonate.

  As the hydrogen carbonate metal salt, alkali metal hydrogen carbonate salts such as potassium hydrogen carbonate and sodium hydrogen carbonate are preferable. The hydrogencarbonate metal salt may be used alone or in combination of two or more kinds.

  The content of the hydrogen carbonate metal salt is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 0.8% by mass or more, in 100% by mass of the volatile rust preventive agent. Is. When the content of the hydrogencarbonate metal salt is within this range, the long-term rust preventive performance becomes good. The content of hydrogencarbonate metal salt is preferably 20% by mass or less, and more preferably 10% by mass or less. When the content of the hydrogencarbonate metal salt is within this range, the rust preventive action by the hydrometathesis reaction of the nitrite and the ammonium salt is effectively exhibited.

  Further, the content of the hydrogen carbonate metal salt is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and 20 parts by mass with respect to 100 parts by mass of the total amount of the nitrite salt and the ammonium salt. It is preferably not more than 10 parts by mass, more preferably not more than 10 parts by mass.

  The nitrite-based vaporizable rust preventive agent may contain a water retention aid. In the nitrite-based vaporizable rust preventive agent, the water retention aid has a property of retaining or continuously releasing water to maintain the humidity in the closed space, and is preferably a fibrous substance. Even when the nitrous acid-based vaporizing rust preventive agent is formed into a tablet shape or a granular shape, the entanglement of the fibers secures the strength of the tablet or the granular material and suppresses the disintegration of these. Examples of the fibrous substance include animal fibers such as wool; vegetable fibers such as cotton, hemp, and cellulose; regenerated fibers; synthetic fibers such as viscose rayon; activated carbon fibers, and the like. Vegetable fibers are preferable, and cellulose is preferable. More preferable. Further, the water retention aid is preferably in powder form from the viewpoint of efficiently retaining and releasing water even when the nitrous acid-based vaporizable rust preventive is formed into a tablet form or a granular form.

  The content of the water retention aid is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more in 100% by mass of the volatile anticorrosive agent. It is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less. Further, the content of the water retention aid is preferably 0.01 parts by mass or more and 20 parts by mass or less, more preferably 0.05 parts by mass with respect to 100 parts by mass of the total amount of ammonium salt and nitrite. The amount is 10 parts by mass or less and more preferably 0.1 parts by mass or more and 5 parts by mass or less. When the content of the water retention aid is within this range, the amount of water in the volatile rust preventive agent can be maintained at an appropriate level, and an excellent rust preventive action can be exhibited for a long period of time.

  The nitrite-based vaporizable rust preventive may further contain a binder. The binder is present between the above components and has a function of preventing these components from being separated from each other, which can improve the shape retention of the nitrite-based vaporizing rust preventive agent, and can be used in the form of tablets or tablets. Even when it is formed into a granular shape, it is possible to prevent these from collapsing and ensure long-term rust preventive performance. In addition, the binder has a role of preventing moisture from invading the nitrite-based vaporizing rust preventive agent at once, and a role of preventing excessive contact between other components, so that long-term rust preventive action can be achieved. It exerts the function of enhancing the lasting effect more effectively. Examples of the binder include solid fats and oils [solid fats and oils at room temperature (10 to 40 ° C.)], vegetable wax, animal wax, synthetic resin, and the like. These may be used alone or in combination of two or more. Among them, solid fats and oils are preferable, and powdery solid fats and oils at room temperature (10 to 40 ° C.) are more preferable.

  When the binder is contained, its content is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more in 100% by mass of the volatile rust preventive agent. It is preferably 50% by mass or less, and more preferably 40% by mass or less. The content of the binder is preferably 1 part by mass or more and 100 parts by mass or less, and more preferably 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass as the total of the nitrite salt and the ammonium salt.

  The nitrite-based vaporizable rust preventive agent may be in the form of powder, or may be formed in the form of tablets or granules. Among them, the tablet form is preferable. In the present invention, powdery means a shape having a maximum diameter of less than 100 μm, granular means a shape having a maximum diameter of 100 μm or more and less than 1 mm, and tablet-like means a shape having a maximum diameter of 1 mm or more. It shall be. Further, the shape of the tablet includes pellets, rods, donuts, and the like, and the powder includes granules and the like. Further, the nitrite-based vaporizable rust preventive agent may include the above-mentioned components in one agent, or may be composed of two or more agents including one or more of the above-mentioned ingredients. .

  When the nitrous acid-based vaporizable rust preventive agent is molded into a tablet or granule, the weight of one unit is preferably 0.1 g or more and 0.5 g or less.

  The amount of the nitrous acid-based vaporizable rust preventive agent to be used may be appropriately determined within a range where the rust preventive effect is exhibited. Can be

  In the method of the present invention, the iron-based member and the nitrite-based vaporizable rust preventive agent are allowed to coexist in a closed space adjusted to have low humidity. The temperature at that time is not particularly limited, but may be, for example, room temperature, specifically, 5 ° C. or more and 50 ° C. or less. However, since it is considered that the higher the temperature is, the larger the amount of nitrite ion released from the nitrite-based vaporizing rust preventive agent is, the temperature is preferably 15 ° C or higher or 20 ° C or higher, more preferably 25 ° C or higher, and 40 C. or less is preferable. Of course, within the above temperature range, it is possible to coexist the iron-based member and the nitrite-based vaporizable rust preventive agent at room temperature.

  The time for allowing the iron-based member and the nitrite-based vaporizable rust preventive agent to coexist in a closed space adjusted to low humidity may be appropriately adjusted within a range in which the rust preventive effect is sufficiently obtained, but is, for example, 1 day or more. It is possible, and 1 week or more is desirable, 2 weeks or more is more desirable. The upper limit is not particularly limited, and the iron-based member may be distributed in the market while being held in a closed space. For example, 3 years or less, 2 years or less, 1 year or less, 6 months or less, 2 months or less , Or less than 1 month.

  According to the method of the present invention, an excellent passivation film can be effectively formed on the surface of the iron-based member by the above steps. As a result, the rust preventive effect continues even after the iron-based member is taken out from the closed space.

  Conventionally, when trying to evaluate the rust-prevention effect by the natural potential of a rust-prevented iron-based material test piece, the corrosion of the iron-based material test piece progresses even in the electrolyte solution for measuring the natural potential. The spontaneous potential of the test piece could not be measured, and accurate evaluation could not be performed. On the other hand, the present inventors, while degassing the electrolyte solution, by immersing the electrode made of an iron-based material and the reference electrode in the electrolyte solution, by measuring the potential difference between the electrodes, the surface potential of the iron-based material electrode It was also found that it was possible to stabilize and make accurate measurements. It is considered that the reason is that deaeration of the electrolyte solution reduces the amount of dissolved oxygen, which is one of the causes of corrosion of the iron-based material electrode.

  The iron-based material electrode for measuring the natural potential is made of the same material as the iron-based member that is the object of rust prevention and has been rust-proofed under the same conditions, except that it has a shape suitable for measurement.

  The electrolyte that is a solute of the electrolyte solution is not particularly limited as long as it is suitable for measuring the self-potential, and examples thereof include sodium sulfate and potassium sulfate. The concentration of the electrolyte in the electrolyte solution may be appropriately adjusted, and can be, for example, 0.0005 mass% or more and 1 mass% or less.

  As the degassing condition of the electrolyte solution, general conditions can be adopted. For example, an inert gas such as nitrogen gas or argon gas may be blown into the electrolyte solution for bubbling. The amount of the inert gas blown in can be, for example, 50 mL / min or more and 300 mL / min or less.

  The potential difference between the reference electrode and the iron-based material electrode can be measured using a general potentiostat. The spontaneous potential of the iron-based material electrode is preferably obtained when the potential difference becomes stable while observing the potential difference between the two electrodes with a potentiostat.

  By the manufacturing method according to the present invention, an excellent passivation film is formed on the surface of the iron-based member, and its spontaneous potential is increased. For example, the difference in surface potential of the iron-based member that has undergone the rust-prevention step with respect to the surface potential of the iron-based member that has not undergone the rust-prevention step according to the present invention is preferably +90 mV or higher, more preferably +95 mV or higher, and +100 mV. The above is more preferable.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples as well as the present invention, and may be appropriately modified within a range compatible with the gist of the preceding and the following. Of course, it is possible to carry out, and all of them are included in the technical scope of the present invention.

Example 1
(1) Anticorrosion treatment The humidity inside the sealable glass bottle was adjusted using an aqueous glycerin solution. The glass bottle was placed in a room where the temperature was adjusted to 25 ° C between 8:30 and 20:30. When the temperature was stable at 25 ° C., the relative humidity in the glass bottle was measured by a temperature / humidity recorder installed in the glass bottle. In addition, the temperature inside the room was not adjusted except the above time, and the room temperature was kept.
Separately, a conductor wire was connected to the side surface of a chrome-molybdenum steel (SCM435) cylinder having a cross-sectional diameter of 10 mm and a height of 10 to 20 mm, and it was confirmed that conduction could be established between one cross section. The surfaces other than the cross section where conduction was confirmed were covered with an epoxy resin for insulation. The exposed section was wet-polished with emery paper up to # 2000.
In each glass bottle of which internal humidity was adjusted, one 250 mg tablet of a commercially available vaporizable rust preventive agent (“CHIRES DIA ^(R) A” manufactured by CREST) was placed per 1 L of the glass bottle, and the temperature was the same as above. Hold over night. Next, the chromium-molybdenum steel test material was put in and held for 1 week under the same temperature condition.

(2) Self-potential measurement 0.01 mass% sodium sulfate aqueous solution (300 mL) was put into an electrochemical measurement cell, and nitrogen gas was introduced at a flow rate of 100 mL / min while bubbling, while the above-mentioned test material and reference electrode were used as electrodes. As a result, the Ag / AgCl electrode was dipped, and the spontaneous potential was measured at 35 ° C. using a potentiostat (“VSP” manufactured by Bio-logic Science Instruments). After confirming that the self-potential was stabilized by continuously measuring the self-potential for 1 hour or more, the self-potential of each test material was specified.
Separately, the spontaneous potential was similarly specified using the test material not subjected to the rust-prevention treatment as a control example, and the potential difference from the test material subjected to the rust-prevention treatment was calculated. The results are shown in Table 1.

  As shown above, the potential difference from the control example exceeded +100 mV when rust-preventing treatment was performed with a nitrous acid-based vaporizing rust preventive agent at a relative humidity of 45% RH or less. It was confirmed that the material had a good passivation film formed on the surface and suppressed the anodic reaction, so that it was difficult to corrode.

Example 2
Since the amount of the vaporizable rust preventive agent used in Example 1 was larger than the standard amount, the experiment was repeated with the standard amount used.
Specifically, the above Example except that a commercially available vaporizing rust preventive 250 mg tablet (“CHIRES DIA ^(R) A” manufactured by CREST) was crushed and 56 mg of the vaporizable rust preventive powder was put in an 8 L glass bottle. In the same manner as in No. 1, rust prevention treatment and spontaneous potential measurement were performed. Table 2 shows the results.

  As shown in the results shown in Table 2, even when the amount of the vaporizable rust preventive agent used is standard, the nitrite type vaporizable rust preventive agent is subjected to the rust preventive treatment under the relative humidity of about 40% RH or less. When carried out, the potential difference from the control example was about +100 mV or more, and the excellent passivation film was formed on the surface of the chromium-molybdenum steel test material, and the anode reaction was suppressed. A tendency was observed.

Example 3
As a test piece, a disc-shaped chrome molybdenum steel (SCM435) having a diameter of 52 mm and a thickness of 10 mm was used. The surface of this test piece was polished by a wet polishing machine, degreased with alkali, and washed with ethanol.
The internal humidity in the 5 L glass container was adjusted to 30% RH using a glycerin aqueous solution, and placed in a room adjusted to 25 ° C. for 24 hours overnight to stabilize the humidity. In the glass container, five commercially available vaporizable rust preventive 250 mg tablets ("CHIRES DIA ^(R) A" manufactured by CREST) were placed, and the mixture was kept under the same temperature condition as above overnight. Then, the above-mentioned test piece was put in and kept under the same temperature condition for 2 weeks to obtain a vapor-phase rustproof test piece. In addition, the disc-shaped chromium molybdenum steel that was only polished and washed as described above was subjected to the following rust prevention test as a control sample.
Next, prepare two 500 mL sealed containers, put 50 mL of distilled water in each container, put the vapor phase rust treated test piece in one container, put the control test piece in the other container and close each container. Then, it was left indoors for 28 days. This room was in an air conditioner environment where the temperature was set to 18 ° C. during the day from 8:00 to 20:00, and the air conditioner was turned off during the night from 20:00 to 8:00 the next day, and temperature control was not performed. The minimum temperature at night varies depending on the day, but was actually 7 to 11 ° C. The appearance photograph of the test piece is shown in FIG.
As shown in the results shown in FIG. 1, when the vapor-phase anticorrosive treatment according to the present invention was not performed (control example), severe corrosion was confirmed. On the other hand, no clear corrosion was confirmed on the surface of the test piece which was subjected to the vapor phase rust prevention treatment according to the present invention. As described above, it became clear that the corrosion resistance performance of the iron-based member was remarkably improved by the vapor-phase rust preventive treatment according to the present invention.

Claims (8)

A method for manufacturing an iron-based member, comprising:
A method comprising the step of allowing the iron-based member and a nitrite-based vaporizable rust preventive agent to coexist in a closed space adjusted to have low humidity.   The method according to claim 1, wherein the relative humidity in the closed space is 45% or less.   The nitrite-based vaporizable rust inhibitor contains one or more nitrites selected from the group consisting essentially of dicyclohexylamine nitrite, diisopropylamine nitrite, sodium nitrite, and potassium nitrite. The method according to Item 1 or 2.   The method according to any one of claims 1 to 3, wherein the nitrite-based vaporizable rust inhibitor contains an ammonium salt.   The method according to any one of claims 1 to 4, wherein the iron-based member and the nitrite-based vaporizable rust inhibitor are allowed to coexist for 1 day or more.   The method according to any one of claims 1 to 5, wherein the temperature at which the iron-based member and the nitrite-based vaporizable rust inhibitor coexist is 5 ° C or higher and 50 ° C or lower.   The method according to any one of claims 1 to 6, wherein a difference in surface potential of the iron-based member that has been subjected to the above step with respect to a surface potential of the iron-based member before being subjected to the step is +90 mV or more. A method for measuring the spontaneous potential of an iron-based material, comprising:
A method comprising immersing an electrode made of the iron-based material and a reference electrode in an electrolyte solution while deaerating the electrolyte solution, and measuring a potential difference between the electrodes.